Let's look at the query plan
db.cities
.find( { country_code: 'GB', population: { $gte: 500000 } } )
.*explain("executionStats)*;
Some stats about the query itself:
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "demo.cities",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"country_code" : {
"$eq" : "GB"
}
},
{
"population" : {
"$gte" : 500000
}
}
]
},
The chosen query plan:
"winningPlan" : {
*"stage" : "FETCH",*
"inputStage" : {
*"stage" : "IXSCAN",*
*"keyPattern" : { "country_code" : 1, "population" : 1 },*
"indexName" : *"country_code_1_population_1",*
"isMultiKey" : false,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
*"direction" : "forward",*
"indexBounds" : {
"country_code" : [ "[\"GB\", \"GB\"]" ],
"population" : [ "[500000.0, inf.0]" ]
}
}
},
All the other considered plans:
"rejectedPlans" : [ ... ]
},
Statistics from the execution:
"executionStats" : {
*"nReturned" : 4,*
"executionTimeMillis" : 12,
*"totalKeysExamined" : 4,*
*"totalDocsExamined" : 4,*
"executionStages" : {
"stage" : "FETCH",
*"nReturned" : 4,*
"executionTimeMillisEstimate" : 10,
"inputStage" : {
"stage" : "IXSCAN",
*"nReturned" : 4,*
"executionTimeMillisEstimate" : 10,
"direction" : "forward",
"indexBounds" : {
"country_code" : [ "[\"GB\", \"GB\"]" ],
"population" : [ "[500000.0, inf.0]" ]
},
*"keysExamined" : 4,*
}
}
},
And some server info:
"serverInfo" : {
"host" : "whisky",
"port" : 27017,
"version" : "3.3.8",
"gitVersion" : "00ed8f3b275971093ddd2ee7d3ab558904e28af0"
},
"ok" : 1
}